Nanotube modified solder thermal intermediate structure, systems, and methods

TECHNICAL FIELD

0001The subject matter relates generally to thermal intermediate structures, systems, and methods used to assist in transferring heat from one element or body, such as a circuit, to another, such as a heat sink.

BACKGROUND INFORMATION

0002Electronic components, such as integrated circuits, may be assembled into component packages by physically and electrically coupling them to a substrate. During operation, the package may generate heat which can be dissipated to help maintain the circuitry at a desired temperature. Heat sinks, including heat spreaders, may be coupled to the package using a suitable thermal intermediate structure to assist in transferring heat from the package to the heat sink.

BRIEF DESCRIPTION OF THE DRAWINGS

0003<figref idref="DRAWINGS">FIG. 1</figref> illustrates an embodiment of a thermal intermediate structure placed between an electronic circuit die and a heat sink according to various embodiments;

0004<figref idref="DRAWINGS">FIGS. 2A and 2B</figref> are views in enlarged and schematic form of an embodiment of carbon nanotubes used in the thermal intermediate structure;

0005<figref idref="DRAWINGS">FIG. 3</figref> is a view showing randomly aligned carbon nanotubes in solder;

0006<figref idref="DRAWINGS">FIG. 4</figref> illustrates a process for alignment of carbon nanotubes for use in the thermal intermediate structure;

0007<figref idref="DRAWINGS">FIG. 5</figref> is a view showing a thermal intermediate blank cut from the rolled billet of <figref idref="DRAWINGS">FIG. 4</figref>;

0008<figref idref="DRAWINGS">FIGS. 6–7</figref> are flow charts illustrating methods according to various embodiments; and

0009<figref idref="DRAWINGS">FIG. 8</figref> is a depiction of a computing system according to an embodiment.

DETAILED DESCRIPTION

0010In the following detailed description of various embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that compositional, structural, and logical substitutions and changes may be made without departing from the scope of this disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

0011Examples and embodiments merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The following description is, therefore, not to be taken in a limiting sense.

0012<figref idref="DRAWINGS">FIG. 1</figref> is a cross-section elevation view of an apparatus <b>10</b> according to various embodiments. Apparatus <b>10</b> includes a package substrate <b>12</b>, a die <b>14</b> and a thermal management aid such as a heat sink or an integral heat spreader <b>16</b> which is mounted adjacent the die <b>14</b> and separated from it by a gap.

0013In an embodiment, the substrate of die <b>14</b> is made of silicon and has frontside and backside surfaces. The die <b>14</b> also has an integrated circuit <b>20</b> and solder bump contacts <b>22</b> on the frontside surface. The contacts <b>22</b> connect with contact pads (not shown) on the upper surface of package substrate <b>12</b>. In some embodiments, the contacts <b>22</b> are manufactured according to a commonly used controlled collapse chip connect (C<b>4</b>) process.

0014In use, electric signals and power are provided to the integrated circuit <b>20</b>. Operation of the integrated circuit <b>20</b> causes heating of die <b>14</b>. Heat is transferred from the integrated circuit <b>20</b> through the substrate of die <b>14</b> to the heat spreader <b>16</b> through a thermal intermediate structure <b>24</b> interposed in the gap between them. In an embodiment a buffer layer <b>18</b> is interposed between thermal intermediate structure <b>24</b> and heat sink <b>16</b>.

0015Carbon nanotubes have a coefficient of thermal conductivity along their longitudinal axis which is relatively high relative to their conductivity along a path oriented orthogonal to the longitudinal axis. The thermal conductivity of carbon nanotubes along their longitudinal axes is substantially higher than that of other materials used for thermal intermediates. The thermal conductivity of multi-walled nanotubes is about 3000 to 4000 W/m-K and theoretically about 6000 W/m-K for single walled nanotubes.

0016In an embodiment, the thermal intermediate structure <b>24</b> comprises a plurality of either multi-walled or single walled carbon nanotubes or a combination of both single and double walled nanotubes which are blended with solder. In an embodiment, the carbon nanotubes are chemically bonded to the solder. In an embodiment, the carbon nanotubes are distributed through a matrix of solder and make up a volume percentage the total less than about 5% to 50% of the volume of the composition by weight.

0017In an embodiment, the solder material is indium which has a thermal conductivity of at least about 85 W/mK. While in one embodiment a solder formed of an indium alloy could have a high thermal conductivity, other solder alloys generally have thermal conductivities of 30 W/mK or lower.

0018Forming a blend of carbon nanotubes and solder or a distribution of carbon nanotubes in a solder matrix is complicated due to the low wetting of nanotubes to most solders. In one embodiment, chemical bonding of the solder to carbon nanotubes of the plurality of carbon nanotubes is facilitated by pre-coating some of the carbon nanotubes prior to blending them with the molten solder.

0019In one embodiment, prior to the blending of the carbon nanotubes with the solder, at least some of the carbon nanotubes <b>28</b> of the thermal intermediate structure <b>24</b> are pre-coated or partially pre-coated with a metal is selected from the group consisting of gold, platinum, silver or palladium and alloys comprising one or more of gold, platinum, silver and palladium, or other suitable metals or alloys, by physical deposition or sputtering methods which are known.

0020In one embodiment, the coated nanotubes <b>28</b> are also referred to as decorated with the coating metal. The metal decorations on the nanotubes provide a wetting contact between the nanotubes and the solder to improve the bond between the solder and the nanotubes and further reduce the contact thermal resistance between nanotubes of the thermal intermediate structure <b>24</b> and either the surface of die <b>14</b> or of heat spreader <b>16</b>.

0021In one embodiment, incorporation of metal particles <b>32</b> at various points distributed along the body of some nanotubes <b>28</b> of the plurality of nanotubes should improve the wetting of the nanotubes with solder surrounding those nanotubes. In one embodiment shown in <figref idref="DRAWINGS">FIG. 2A</figref>, a known process for decorating carbon nanotubes with gold, platinum, palladium or silver involves an initial refluxing of nanotubes with nitric acid to open closed tips of the tubes <b>28</b> and to create acid sites <b>30</b> on the surface of nanotubes <b>28</b> to act as nucleation centers for metal ions. Refluxing the nanotubes in the presence of a reducing agent such as HAuCl₄results in <figref idref="DRAWINGS">FIG. 2B</figref> with gold particles <b>32</b> forming at the nucleation sites to produce decorated carbon nanotubes. Similarly, in an embodiment, a reducing agent H₂PtCl₆is used to decorate the nanotubes with platinum. Similar processes can also be used to incorporate palladium or silver with acid opened nanotubes.

0022The acid sites <b>30</b> which receive the metal decorations <b>32</b> are understood to be generally dispersed over the body of the nanotubes <b>28</b> rather than along fault lines as would be expected in the case of metal decoration of graphite crystals, for example.

0023In one embodiment, electrochemical means of coating nanotubes with metal decorations can be utilized. In one embodiment, coating a second metal on the nanotube for alloying purposes as part of the metal decoration process can be utilized.

0024In one embodiment, other physical methods such as sputtering can be used to produce metal coated carbon nanotubes.

0025Decorating the carbon nanotubes <b>28</b> with metals <b>32</b> to improve the wetting of the nanotubes for forming a chemical bond between the solder <b>28</b> and the decorated nanotubes. In one embodiment, alignment of the nanotubes along the shortest heat transfer path will contribute to maximizing the thermal performance of the thermal intermediate structure <b>24</b>. In <figref idref="DRAWINGS">FIG. 1</figref>, the shortest path for heat flow from die <b>14</b> to heat spreader <b>16</b> is along paths perpendicular to the surfaces of die <b>14</b> and heat spreader <b>16</b> which engage thermal intermediate structure <b>24</b>.

0026In <figref idref="DRAWINGS">FIG. 3</figref>, a portion of a thermal intermediate structure <b>24</b> according to an embodiment is shown in enlarged schematic form with a plurality of carbon nanotubes <b>28</b> somewhat randomly oriented in the matrix of solder <b>29</b> into which they are mixed.

0027In one embodiment, some of the carbon nanotubes <b>28</b> of the plurality of carbon nanotubes are to be aligned in an x, y plane by successive rolling and folding operations performed on the solder <b>29</b> and carbon nanotube <b>28</b> composite material.

0028In <figref idref="DRAWINGS">FIG. 4</figref>, a billet of indium solder which has incorporated within it a plurality of single walled nanotubes or of multiple walled nanotubes, is rolled or extruded along an axis <b>33</b> to align at least some nanotubes <b>28</b> of the plurality of nanotubes with each other and generally parallel to axis <b>33</b> as shown in <figref idref="DRAWINGS">FIG. 4</figref> forming a billet <b>35</b> of solder material with blended nanotubes generally aligned with each other and parallel to axis <b>33</b>.

0029Indium is well adapted to such rolling and folding operations because it is soft and easily workable. The mixture of nanotubes <b>28</b> which are incorporated into the solder <b>29</b> do not materially detract from the mechanical workability of billet <b>35</b>. In an embodiment, the density of nanotubes <b>28</b> in the solder <b>29</b> is less than about 5 to 30% by volume and is in some cases up to 50% by volume. In <figref idref="DRAWINGS">FIG. 5</figref>, a thermal intermediate blank <b>38</b> sliced from billet <b>35</b> of <figref idref="DRAWINGS">FIG. 4</figref> along one of a series of transverse cutting lines formed at one of a series of longitudinal slicing points <b>36</b>, is shown after being rotated by 90° from its alignment illustrated in <figref idref="DRAWINGS">FIG. 4</figref>. After a plurality of blanks <b>35</b> of solder/carbon nanotube composite are formed, the thin sections or blanks <b>35</b> are bonded together to achieve orientation of some of the plurality of carbon nanotubes in the z axis, normal to the heat sink <b>16</b> surface and the surface of die <b>14</b>, for improved heat flow between the die and heat sink. One or more of such blanks <b>38</b> make up the thermal intermediate structure <b>24</b>.

0030In one embodiment, extrusion or pultrusion of a rolled indium billet <b>35</b> is followed by slicing and rotating the slice to provide orientation of a high number of carbon nanotubes of the plurality of carbon nanotubes <b>28</b> in the z-axis.

0031Some embodiments include a number of methods. For example, <figref idref="DRAWINGS">FIG. 6</figref> is a flow chart illustrating several methods according to various embodiments. Thus, a method <b>611</b> may (optionally) begin at block <b>621</b> with forming a billet <b>35</b> of solder <b>29</b> incorporating a plurality of carbon nanotubes <b>28</b> therein which are chemically bonded to the solder. The method includes, at block <b>631</b>, aligning a substantial percentage of the carbon nanotubes with an axis of the billet by successive rolling operations. In one embodiment in the method at block <b>631</b>, the aligning a substantial number of the carbon nanotubes includes working the billet by a process selected from the group consisting of rolling extruding or pultruding to align some carbon nanotubes <b>28</b> of the plurality of carbon nanotubes with axis <b>33</b> (<figref idref="DRAWINGS">FIG. 4</figref>) along which the working of the billet <b>35</b> occurs.

0032In one embodiment, the method includes, in block <b>641</b>, slicing the billet perpendicular to the axis <b>32</b> into thermal intermediate blanks <b>38</b> having a thickness substantially less than their length or width. The thermal intermediate blanks <b>38</b> are then assembled into a thermal intermediate structure <b>24</b> having a substantial percentage of the carbon nanotubes of plurality of carbon nanotubes <b>28</b> aligned.

0033In an embodiment, in block <b>651</b>, the thermal intermediate structure <b>24</b> is interposed in a gap between a die <b>14</b> and a heat sink <b>16</b>. In an embodiment, the gap between the die and the heat sink is less than or equal to about 20 microns. In other embodiments the gap may be as large as from about 150 to about 250 microns or as small as 5 microns.

0034<figref idref="DRAWINGS">FIG. 7</figref> is a flow chart of a method <b>710</b> illustrating several methods according to various embodiments. Thus, method <b>710</b> may (optionally) begin at block <b>721</b> with forming a thermal intermediate structure comprised of a plurality of metal decorated carbon nanotubes <b>28</b> blended into a solder material <b>29</b> with at least some of the plurality of carbon nanotubes <b>28</b> substantially aligned with an axis <b>32</b> of billet <b>35</b>.

0035In an embodiment, the method includes, in block <b>731</b>, coupling a first surface of the thermal intermediate structure to a surface of a heat sink with the surface of the thermal intermediate structure oriented substantially perpendicular to the surface of the heat sink. In one embodiment, the method includes, in block <b>741</b>, coupling a second surface of the thermal intermediate structure to a surface of the heat source

0036In an embodiment, the process in block <b>731</b> of coupling a first surface of the thermal intermediate structure <b>24</b> to a surface of a heat sink <b>16</b> also comprises forming a solder bond between the surface of the heat source <b>14</b> and the second surface of the thermal intermediate structure <b>24</b>. In one embodiment, the process in block <b>741</b> of coupling a second surface of the thermal intermediate structure <b>24</b> to a surface of the heat sink <b>16</b> also comprises forming a solder bond between the surface of the heat sink <b>16</b> and the first surface of the thermal intermediate structure <b>24</b>.

0037<figref idref="DRAWINGS">FIG. 8</figref> is a depiction of a computing system according to an embodiment. One or more of the embodiments of apparatus with one or more dies <b>14</b> having a thermal intermediate structure <b>24</b> interposed between the die surface and the heat sink <b>16</b> and comprising a plurality of carbon nanotubes <b>28</b>, some of which are decorated with metal <b>32</b>, the plurality of carbon nanotubes blended with solder <b>29</b> may be used in a computing system such as a computing system <b>800</b> of <figref idref="DRAWINGS">FIG. 8</figref>. The computing system <b>800</b> includes at least one processor (not pictured), which is enclosed in a microelectronic device package <b>810</b>, a data storage system <b>812</b>, at least one input device such as a keyboard <b>814</b>, and at least one output device such as a monitor <b>816</b>, for example. The computing system <b>800</b> includes a processor that processes data signals, and may include, for example, a microprocessor available from Intel Corporation. In addition to the keyboard <b>814</b>, an embodiment of the computing system includes a further user input device such as a mouse <b>818</b>, for example.

0038For the purposes of this disclosure, a computing system <b>800</b> embodying components in accordance with the claimed subject matter may include any system that utilizes a microelectronic device package, which may include, for example, a data storage device such as dynamic random access memory, polymer memory, flash memory and phase change memory. The microelectronic device package can also include a die that contains a digital signal processor (DSP), a micro-controller, an application specific integrated circuit (ASIC), or a microprocessor.

0039Embodiments set forth in this disclosure can be applied to devices and apparatus other than a traditional computer. For example, a die <b>14</b> can be packaged with an embodiment of the thermal intermediate structure <b>24</b>, and placed in a portable device such as a wireless communicator or a hand held device such as a personal data assistant or the like. Another example is a die <b>14</b> that can be coupled to a heat sink <b>16</b> with an embodiment of the thermal intermediate structure <b>24</b> and placed in a dirigible craft such as an automobile, a watercraft, an aircraft or a spacecraft.

0040The apparatus <b>10</b>, substrate <b>12</b>, die <b>14</b>, heat spreader <b>16</b>, integrated circuit <b>20</b>, solder bumps <b>22</b> thermal intermediate structure <b>24</b> and metal decorated, aligned nanotubes <b>28</b> may all be characterized as “modules” herein. Such modules may include hardware circuitry, and/or a processor and/or memory circuits, software program modules and objects, and/or firmware, and combinations thereof, as desired by the architect of the apparatus <b>10</b> and system <b>900</b>, and as appropriate for particular implementations of various embodiments. For example, such modules may be included in a system operations simulation package, such as a software electrical signal simulation package, a power usage and distribution simulation package, a thermo-mechanical stress simulation package, a power/heat dissipation simulation package, and/or a combination of software and hardware used to simulate the operation of various potential embodiments.

0041It should also be understood that the apparatus and systems of various embodiments can be used in applications other than for coupling and heat transfer between die and heat sinks and thus, these embodiments are not to be so limited. The illustrations of apparatus <b>10</b> and system <b>800</b> are intended to provide a general understanding of the elements and structure of various embodiments, and they are not intended to serve as a complete description of all the features of compositions, apparatus, and systems that might make use of the elements and structures described herein.

0042Applications that may include the novel apparatus and systems of various embodiments include electronic circuitry used in high-speed computers, communication and signal processing circuitry, data transceivers, modems, processor modules, embedded processors, and application-specific modules, including multilayer, multi-chip modules. Such apparatus and systems may further be included as sub-components within a variety of electronic systems, such as televisions, cellular telephones, personal computers, workstations, radios, video players, vehicles, and others.

0043It should be noted that the methods described herein do not have to be executed in the order described, or in any particular order. Moreover, various activities described with respect to the methods identified herein can be executed in serial or parallel fashion.

0044Although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. It is to be understood that the above description has been made in an illustrative fashion, and not a restrictive one. Combinations of the above embodiments, and other embodiments not specifically described herein will be apparent to those of skill in the art upon reviewing the above description. Thus, the scope of various embodiments includes any other applications in which the above compositions, structures, and methods are used.

0045It is emphasized that the Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate preferred embodiment. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively. Moreover, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.